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In this article we will discuss about:- 1. Habitat and Morphology of Entamoeba Histolytica 2. Nutrition Required by Entamoeba Histolytica 3. Life-Cycle.
Habitat and Morphology of Entamoeba Histolytica:
Entamoeba histolytica is a parasite and lives in the mucous and sub-mucous layers of the large intestine of man. It may occur in the liver and lungs. Rarely it invades brain, spleen etc. causing ulcers. The disease caused by the parasite is known as “Amoebic dysentery.”
It occurs in two forms—Trophic and Cystic.
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a. Trophic:
The trophic forms vary in size from 15-40 micro average being 25 micro. The cell body is divisible into two distinct portions—ectoplasm and endoplasm. The ectoplasm is clear and translucent while the endoplasm is granular. The endoplasm often contains ingested red blood corpuscles. The pseudopodia may be long, finger like or rounded in shape. In freshly passed stool the parasite shows a single pseudopodium (Fig. 50A).
The nucleus is indistinct in living condition but in stained preparation it shows a central Karyosome or Endosome and a uniform ring of peripheral chromatid granules. The nuclear membrane is very delicate. The nucleus is 4-6 micro in diameter.
b. Cyst:
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Cysts vary in diameter from 10-20 micro. The cysts are spherical. The cyst wall is double and the cytoplasm usually bears four nuclei. The cytoplasm is clear and often contains black rod-like chromatoid bar or bodies. Presence of these bodies is the characteristic of E. histolytica cyst. They occur singly or in multiples of two.
Nutrition Required by Entamoeba Histolytica:
The parasite gets its nutrition from the red blood cells and tissue cells of their host. They produce a toxic substance which dissolve the mucous and sub-mucous layers of the large intestine. From the resultant absess it derives its nutrition. This is evident from the fact that the stool of persons with amoebic dysentery contain pure blood and mucus.
Life-Cycle of Entamoeba Histolytica:
Entamoeba histolytica multiplies by binary fission in the trophic stage. They have the capacity to encyst. Prior to encystment the parasite rounds up and eliminates food vacuoles. A cyst wall develops and the nucleus divides first into 2 and then into 4.
The quadrinucleate cyst is the infective stage. It comes out with the feces of the host. Through contaminated food or drink the infective cysts pass into the lower portion of the small intestine of the new host.
There the cyst wall dissolves by the action of the intestinal enzymes and a 4 nucleate amoeba emerges. Division of both the cytoplasm and the nuclei of the amoeba results 8 small amoebulae. They become active and transform into trophic form (Fig. 50B).
